docs: def action_cancel(self):
          """Set a change request as cancelled."""
          self.write({'state': 'cancelled'})
          for rec in self:
              rec.message_post(
                  subtype='mt_comment',
                  body=_(
                      'Change request <b>%s</b> has been cancelled by %s.'
                      ) % (rec.display_name, self.env.user.name)
                  )